1. Field of the Invention
The present invention relates to a display device, and more particularly, to a liquid crystal display device (LCD). Although the present invention is suitable for a wide scope of applications, it is particularly suitable for preventing a short circuit between a circuit part and a common electrode of a liquid crystal panel.
2. Description of the Related Art
As the information society develops, display device technology is at the forefront of human-machine or human-human communication. The increasing use of computer and other visual media equipment is increasing the demand for light and thin flat-panel display devices. Of the flat-panel display devices, an LCD is widely used as a monitor in a notebook or a desktop computer because the LCD can be driven at a low voltage and has excellent resolution, color rendering, and image quality.
The LCD includes two substrates each having electrodes for electric field generation. The two substrates are disposed such that their surfaces, where the electrodes are formed, face each other and a liquid crystal material is injected between the two substrates. Then, the orientation of the long thin liquid crystal molecules of the liquid crystal material is controlled by a voltage applied to the two electrodes, thereby controlling light transmittance. When individual pixels are controlled in such a manner corresponding to image data, the LCD displays an image.
FIG. 1 is a schematic perspective view of a related art liquid crystal panel, and FIG. 2 is a cross-sectional view of region A′ in FIG. 1. As illustrated in FIG. 1, the liquid crystal panel 505 includes a lower substrate 550 provided with a plurality of devices (not shown), an upper substrate 510 provided with color filters (not shown), and a sealant 600 bonding the upper substrate 510 and the lower substrate 550 together. The sealant 600 is formed at the edges of the two substrates. The lower substrate 550 is larger than the upper substrate 510 such that a data pad part 630 connected to a driving circuit for driving the liquid crystal panel 505 is provided at an edge of the lower substrate 550 of the liquid crystal panel 505 outside of the upper substrate 510. Also, a gate circuit part 620 can be provided at another edge of the lower substrate 550 outside of the upper substrate 510.
As shown in FIG. 2, the liquid crystal panel 505 includes a pixel region (active area—A/A) 610 for displaying an image. The lower substrate 550 of the pixel region 610 includes a plurality of gate lines (not shown) and a plurality of data lines (not shown) crossing each other at a right angle, a thin film transistor (TFT) provided at each crossing, and pixel electrodes provided in regions defined by the gate lines and the data lines. The upper substrate 510 of the pixel region 610 includes color filters for implementing colors, a black matrix 520 for preventing light crosstalk, and a common electrode 530 facing each of the pixel electrodes provided on the lower substrate 550.
A line on glass (LOG) technology is used in the gate circuit part 620 such that a gate drive IC is formed directly on the lower substrate 550. The data pad part 630 includes data pad lines (not shown) transferring an image signal supplied from a data driver integrated circuit (not shown) to the data line of the pixel region 610. The data driver integrated circuit (IC) is mounted on a tape carrier package (TCP) and is connected to the data pad part 630 of the lower substrate 550 by a TAB method.
As shown in FIG. 2, a sealant 610 bonds the upper substrate 510, including the black matrix 520 and the common electrode 530, to the lower substrate 550, including an array layer 555 having the TFT and the pixel electrode. Signal lines 570 of the gate circuit part 620 are connected to the gate lines of the pixel region 610 by connection lines (not shown) on the lower substrate 550 to supply a gate driving signal generated from the gate circuit part 620 to the gate lines (not shown) of the pixel region 610. A contact part 580 electrically connected to the connection line (not shown) is exposed to the outside at the signal line region 570 of the gate circuit part 620 of the lower substrate 550. The contact part 580 is formed by removing an insulation film 590 formed on the signal line 570. Thus, a gate signal from the gate circuit part 620 can be supplied to the gate lines of the pixel region 610 through the connection lines.
An electrical shorting problem may occur between the signal lines of the gate circuit part 620 and the common electrode 530 of the upper substrate 510 because of conductive balls 605 included in the sealant 600 used to bond the upper and lower substrates 510 and 550 together. The sealant contains conductive balls to supply a common voltage from the lower substrate 550 to the common electrodes of the upper substrate 510. The reason for the shorting problem is that when the sealant 600 including the conductive balls 605 is applied, some of the conductive balls 605 contact the contact part 570 of the gate circuit part 620 and the common electrode 530 of the upper substrate 510. Consequently, a problem occurs in that gate signals supplied from the gate circuit part 620 leak to the common electrode 530 through the conductive balls 605 or a common voltage applied to the common electrode 530 leaks to a gate line. Such leakage and/or distortion of the common voltage degrades image quality.